Right here goes ...
The Aygo/C1/107 are the same car with only cosmetic differences, mainly between the Aygo and the other 2, the car was developed by toyota and is built in a toyota plant ... citroen and peugeot are 1 company .... called PSA Peugeot Citroen ... and so the C1 / 107 is just 'badge engineering'
Mazda is largely (but not entirely) owned by Ford so the Mazda 2 is to some extent a Fiesta underneath but this is just the platform and not the greenhouse (upper body)
Oh and the New Ka is a Fiat 500 underneath and is going to be produced in a Fiat factory ... and is actually from a Fiat Panda platform
As to them all looking the same ...
well I'd disagree ...
the problem is that you have to balance package/safety/styling/cost not easy on a small car ... but you do get different products ... the Ka, 500, Micra, Corsa, Fiesta, Aygo all look different to me